The present invention relates to turbines suitable for down-hole applications such as bore-hole drilling and driving various down-hole tools.
Conventional turbines for down-hole use generally comprise a longitudinally extending turbine stage array in which the drive fluid passes substantially axially through a multiplicity of turbine stages connected in series. Particular disadvantages of this type of arrangement include relatively low efficiency due to the rapid increase of efficiency losses with increasing number of turbine stages, and the considerable length required to achieve any useful torque levels. Typical commercially available turbines of this type having of the order of 100 to 200 turbine stages, have a length of around 20 m and longer. Such a length presents considerable restrictions on the use of such turbines in non-rectilinear drilling e.g. directional drilling situations, because of restrictions on minimum radius of curvature of kick-off which can be used, as well as in drilling operations using coiled tubing because of the large lubricators required to accommodate the turbine together with the drilling tools and other equipment required. This in turn gives rise to substantial practical problems in the positioning of the injector at a suitable height, above the lubricator.
It is an object of the present invention to avoid or minimise one or more of the above disadvantages and/or problems.
It has now been found that a compact, high power, turbine can be achieved by means of a combined redial impulse and drag turbine in which substantially increased turbine drive output is obtained within a given length of turbine.
The present invention provides a turbine suitable for use in down-hole drilling and the like, and comprising a tubular casing enclosing a chamber having rotatably mounted therein a rotor comprising at least one turbine wheel blade array with an annular array of angularly distributed blades orientated with drive fluid receiving faces thereof facing generally rearwardly of a forward direction of rotation of the rotor, and a generally axially extending inner drive fluid passage generally radially inwardly of said rotor, said casing having a generally axially extending outer drive fluid passage, one of said inner and outer drive fluid passages constituting a drive fluid supply passage and being provided with at least one outlet nozzle formed and arranged for directing at least one jet of drive fluid onto said blade drive fluid receiving faces of said at least one blade array as said blades traverse said nozzle for imparting rotary drive to said rotor, the other constituting a drive fluid exhaust passage and being provided with at least one exhaust aperture for exhausting drive fluid from said at least one turbine wheel blade array.
Preferably the turbine has a plurality, advantageously, a multiplicity, of said turbine wheel means disposed in an array of parallel turbine wheels extending longitudinally along the central rotational axis of the turbine with respective parallel drive fluid supply jets.
In a particularly preferred aspect the present invention provides a turbine suitable for use in down-hole drilling and the like, and comprising a tubular casing enclosing a chamber having rotatably mounted therein a rotor having at least two turbine wheel blade arrays each with an annular array of angularly distributed blades orientated with drive fluid receiving faces thereof facing generally rearwardly of a forward direction of rotation of the rotor, and a generally axially extending inner drive fluid passage generally radially inwardly of each said turbine wheel blade array, said casing having a respective generally axially extending outer drive fluid passage associated with each said turbine wheel blade array, one of said inner and outer drive fluid passages constituting a drive fluid supply passage and being provided with at least one outlet nozzle formed and arranged for directing at least one jet of drive fluid onto said blade drive fluid receiving faces as said blades traverse said at least one nozzle for imparting rotary drive to said rotor, the other constituting a drive fluid exhaust passage and being provided with at least one exhaust aperture for exhausting drive fluid from said turbine wheel blade arrays, neighbouring turbine wheel blade arrays being axially spaced apart from each other and provided with drive fluid return flow passages therebetween connecting the exhaust passage of an upstream turbine wheel blade array to the supply passage of a downstream turbine wheel blade array for serial interconnection of said turbine wheel blade arrays.
Instead of, or in addition to providing a said inner or outer drive fluid passage for exhausting of drive fluid from the chamber, there could be provided exhaust apertures in axial end wall means of chamber, though such an arrangement would generally be less preferred due to the difficulties in manufacture and sealing.
In yet another variant of the present invention, both the drive fluid supply and exhaust passage means could be provided in the casing (i.e. radially outwardly of the rotor) with drive fluid entering the chamber from the supply passage via nozzle means to impact the turbine blade means and drive them forward, and then exhausting from the chamber via outlet apertures angularly spaced from the nozzle means in a downstream direction, into the exhaust passages.
Thus essentially the turbine of the present invention is of a radial (as opposed to axial) flow nature with motive fluid moves between radially (as opposed to axially) spaced apart positions to drive the turbine blade means. This enables the performance, in terms of torque and power characteristics, of the turbines of the present invention to be readily varied by simply changing the nozzle sizexe2x80x94without at the same time having to redesign and replace all the turbine blades as is generally the case with conventional axial flow turbines when any changes in fluid velocity and/or fluid density are made. Thus, for example, reducing the nozzle size will (assuming constant flow rate) increase the (fluid jet) flow velocity thereby increasing torque. This will also increase the operating speed of the turbine and thereby the power, as well as increasing back pressure. Similarly increasing flow rate while keeping nozzle size constant will also increase the (fluid jet) flow velocity thereby increasing torque as well as giving an increase in the operating speed of the turbine and thereby the power and increasing back pressure. Alternatively, increasing the nozzle size while keeping the (fluid jet) flow velocity constantxe2x80x94by increasing the flow rate, would increase torque and power without increasing the turbine speed or back pressure. If desired, torque can also be increased by increasing the density of the drive fluid (assuming constant fluid flow rate and velocity) which increases the flow mass.
It will be appreciated that individual nozzle size can be increased longitudinally and/or angularly of the turbine, and that the number of nozzles for the or each turbine wheel blade array can also be varied.
The turbine blades can also have their axial extent longitudinally of the turbine increased so as to increase the parallel mass flow of motive fluid through the or each turbine wheel array, without suffering the severe losses encountered with conventional multi-stage turbines comprising axially extending arrays of axially driven serially connected turbine blade arrays.
Another advantage of the turbines of the present invention that may be mentioned is the circumferential fluid velocity distribution over the turbine blades is, due to the generally radial disposition of the said blades, substantially constant and thus very efficient in comparison with an axial turbine where the velocity distribution varies over the length of the blade and thus losses are caused through hydrodynamic miss-match of fluid velocity and circumferential blade velocity.
The turbines of the present invention also have some significant advantages over positive displacement motors in that they can use relatively viscous and/or dense drive fluids such as more or less heavily weighted drilling muds e.g. high density drilling muds weighted with bentonite or barytes, which are required, for example, for high pressure wells.
Another important advantage over conventional turbines for down-hole use is that the motors of the present invention are substantially shorter for a given output power (even when taking into account any gear boxes which may be required for a given practical application). Typically a conventional turbine may have a length of the order of 15 to 20 meters, whilst a comparable turbine of the present invention would have a length of only 2 to 3 meters for a similar output power. This has very considerable benefits such as reduced manufacturing costs, easier handling, and smaller radius borehole deviation negotiation ability.
Yet another advantage that may be mentioned is that the relatively high overall efficiency of turbines of the present invention allows the use of smaller size (diameter) turbines than has previously been possible. With conventional down-hole turbines, the so called xe2x80x9cslot lossesxe2x80x9d which occur due to drive fluid leakage between the tips of the turbine blades and the casing due to the need for a finite clearance therebetween, become proportionately greater with reduced turbine diameter. In practice this results in a minimum effective diameter for a conventional turbine of the order of around 10 cm. With the increased overall efficiency of the turbines of the present invention it becomes practical significantly to reduce the turbine diameter, possibly as low as 3 cm.
In one, preferred, form of the invention the outer passage means serves to supply the drive fluid to the turbine wheel means via nozzle means, preferably formed and arranged so as to project a drive fluid jet generally tangentially of the turbine wheel means, and the inner passage means serves to exhaust drive fluid from the chamber, with the inner passage means conveniently being formed in a central portion of the rotor. In another form of the invention the inner passage means is used to supply the drive fluid to blade means mounted on a generally annular turbine wheel means. In this case the nozzle means are generally formed and arranged to project a drive fluid jet more or less radially outwardly, and the blade means drive fluid receiving face will tend to be oriented obliquely of a radial direction so as to provide a forward driving force component as the jet impinges upon said face.
In principle there could be used just a single nozzle means. Generally though there is used a plurality of angularly distributed nozzle means e.g. 2, 3 or 4 at 180xc2x0, 120xc2x0 or 90xc2x0 intervals, respectively. In the preferred form of the invention, the nozzle means are preferably formed and arranged to direct drive fluid substantially tangentially relative to the blade means path, but may instead be inclined to a greater or lesser extent radially inwardly or outwardly of a tangential direction e.g. at an angle from +5xc2x0 (outwardly) to xe2x88x9220xc2x0 (inwardly), preferably 0xc2x0 to xe2x88x9210xc2x0, relative to the tangential directionxe2x80x94corresponding to from 95 to 70xc2x0, preferably 90 to 80xc2x0, relative to a radially inward direction.
As noted above the power of the motor may be increased by increasing the motive fluid energy transfer capacity of the turbine, in parallelxe2x80x94e.g. by having larger cross-sectional area and/or more densely angularly distributed nozzles. The driven capacity of the turbine may be increased by inter alia increasing the angular extent of the nozzle means in terms of the size of individual nozzle means around the casing, and/or by increasing the longitudinal extent of the nozzle means in terms of longitudinally extended and/or increased numbers of longitudinally distributed nozzle means. In general though the outlet size of individual nozzle means should be restricted relative to that of the drive fluid supply passage, in generally known and calculable manner, so as to provide a relative high speed jet flow. The jet flow velocity is generally around twice the linear velocity of the turbine (at the fluid jet flow receiving blade portion) (see for example standard text books such as xe2x80x9cFundamentals of Fluid Mechanicsxe2x80x9d by Bruce R Munson et al published by John Wiley and Sons Inc). Typically, with a 3.125 inch (8 cm) diameter turbine of the invention there would be used a nozzle diameter of the order of from 0.1 to 0.35 inches (0.25 to 0.89 cm).
The size of the blade means including in particular the longitudinal extent of individual blade means and/or the number of longitudinally distributed blade means, will generally be matched to that of the nozzle means. Preferably the blade means and support therefor are formed and arranged so that the unsupported length of blade means between axially successive supports is minimised whereby the possibility of deformation of the blade means by the drive fluid jetting there onto is minimised, and in order that the thickness of the blade means walls may be minimised. The number of angularly distributed individual blade means may also be varied, though the main effect of an increased number is in relation to smoothing the driving force provided by the turbine. Preferably there is used a multiplicity of more or less closely spaced angularly distributed blade means, conveniently at least 6 or 8, advantageously at least 9 or 12 angularly distributed blade means, for example from 12 to 24, conveniently from 15 to 21, angularly distributed blade means.
It will also be appreciated that various forms of blade means may be used. Thus there may be used more or less planar blade means. Preferably though there is used a blade means having a concave drive fluid receiving face, such a blade means being conveniently referred to hereinafter as a bucket means. The bucket means may have various forms of profile, and may have open sides (at each longitudinal end thereof). Conveniently the buckets are of generally part cylindrical channel section profile (which may be formed from cylindrical tubing section). Optimally, however, the bucket should be aerodynamically/hydrodynamically shaped to prevent detachment of the boundary layer and to produce a less turbulent flow through the turbine blade array and thus reduce parasitic pressure drop across the blade array.
Various forms of blade support means may be used in accordance with the present invention. Thus, for example, the support means may be in the form of a generally annular structure with longitudinally spaced apart portions between which the blade means extend. Alternatively there may be used a central support member, conveniently in the form of a tube providing the inner drive fluid passage means, with exhaust apertures therein through which used drive fluid from the chamber is exhausted, the central support member having radially outwardly projecting and axially spaced apart flanges or fingers across which the blade means are supported. Alternatively the blade means may have root portions connected directly to the central support member.
The turbines of the present invention may typically have normal running speeds of the order of 3,000 to 10,000, for example, from 5,000 to 8,000, rpm. In order to increase torque they are preferably used with gear box means. In general there may be used gear box means providing at least 5:1, preferably at least 10:1, speed reduction. Conveniently there is used a serially interconnected array of epicyclic gear boxes each having a gearing ratio of the order of 3:1 to 4:1, for example 2 gear boxes each having a ratio of 3:1 would provide an overall ratio of 9:1. Preferably there is used an epicyclic gear box with typically 3 or 4 planet wheels mounted in a rotating cage support used to provide an output drive in the same sense as the input drive to the sun wheel, usually clockwise, so that the output drive is also clockwise. Preferably there is used a ruggedised gear box means with a substantially sealed boundary lubrication system, advantageously with a pressure equalisation system for minimizing ingress of drilling mud or other material from the borehole into the gear box interior.
In a further aspect the present invention provides a turbine drive system suitable for use in downhole drilling and the like comprising at least one turbine of the invention drivingly connected to at least one reducing gearbox.
In yet another aspect the present invention provides a bottom hole assembly comprising at least one turbine of the invention drivingly connected to a tool, preferably via at least one reducing gearbox.
In a still further aspect the present invention provides a drilling apparatus comprising a drill string, preferably comprising coiled tubing, and a bottom hole assembly of the invention wherein the tool comprises a drill bit.